Any time the rotating magnetic disk of a disk drive is brought to a stopped condition, there is no aerodynamic cushion available to float or fly the magnetic head above the surface. To prevent damage to the surface of a magnetic disk whenever not rotating, it is conventional to park the magnetic head/slider in a landing zone so that contact with the disk by the slider will not cause any significant damage and will not destroy magnetically recorded data. However, simply parking the read/write head does not address the possibility that the disk drive might be impacted by a force sufficient to dislodge the actuator from its parked position, and thus moving the slider onto the recording surface of the magnetic disk. Accordingly, it is important that the actuator which positions the slider must be restricted or otherwise held in its parked position to prevent any scratching of the data recording region of the disk surface by slider movement over the surface without an interposed aerodynamic film and minimize stiction between the slider and disk by holding the slider in the landing zone.
Extremely smooth surfaces exist on both the disk surface and the magnetic recording face of the slider attached to the load arm of the actuator. Without the aerodynamic cushion between the slider and the disk surface, the slider will come into contact with the disk surface and stiction may result. Stiction occurs as two very smooth surfaces stick to each other and effectively prevent the removal of one from the other. The stiction forces may be sufficient to prevent the rotation of the disk; but if the disk can be rotated, damage almost certainly will occur to the surface of the disk due to the fact that the slider is in contact with and stuck to the disk surface as the disk moves relative to the slider.
The magnetic recording head/slider can be parked in a landing zone or on an unload device. The actuator which moves the slider must be latched to prevent movement of the slider out of the parked position onto the data recording region of the magnetic disk.
Locking devices commonly are used to retain the actuator and accordingly retain the slider in a position whereby contact of the slider to the disk surface will cause no damage; alternatively, these devices maintain the slider in a position where it is unloaded from the disk surface.
The latching or locking devices previously used typically have been mechanical latches, electromechanical latches and solenoid activated locking devices. Mechanical latches typically are complex and require release mechanisms while the electromechanical latches require substantial electrical power to operate; in battery operated computers, the electrical power drain may severely shorten battery life.
The solenoid lock systems also are relatively large consumers of electrical power and are relatively large in size and thus require a significant number of parts with associated cost and reliability considerations.